Abstract— The effect of water deficit on spring wheat yield (Triticum aestivum L.) was analyzed focusing on crop growth and dry weight partitioning during the spike growth period (SGP). Two levels of water availability (rainfed and irrigated) were tested in two locations (Córdoba and Balcarce, Argentina). The degree of source limitation for grain filling was greater under rainfed conditions (12%) than under irrigation (5%); however, water stress affected yield by 40% (mean of all experiments), mainly through grain number m-2 (GN) rather than by differences in weight per grain. The decrease in GN due to water stress was associated with spikes dry weight (SDW = total spikes weight – grain weight) measured 7 days after anthesis, but some additional experiment effect was detected on GN. Analysis of different weather variables showed the vapor pressure deficit (VPDX) as the one that best explained GN deviations. A model for GN estimation with or without water stress, was developed including the effect of water stress on SDW reduction (), where H represents no water stress:
The SDW was analyzed as the product between spike growth rate (SGR) and the spike growth period (SGP) duration. SGP duration was not affected by water level, but anthesis date was up to 9 days earlier under water stress in Córdoba. SGR was more associated with crop growth rate (CGR) than with assimilates partition to spikes, and this effect increased when CGR was reduced. CGR was associated with the amount of intercepted photosynthetic active radiation during the SGP but not with the radiation use efficiency. Thus, GN was affected for both water stress reducing the availability of assimilates for spike growth and VPDX of each environment.
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